During a heart muscle pumping cycle, which normally lasts for about 500 msec, there is a phase wherein the pumping chamber of the heart (i.e. the left ventricle) is completely enclosed. In this phase, known as the pre-ejection phase, the chamber has been filled with blood, and both the inlet valve and the outlet valve of the chamber are closed. Thus, during the pre-ejection phase, which lasts around 10 msec, the chamber (left ventricle) remains essentially isovolumic.
Anatomically, the heart muscle exerts pressure on blood in the chamber during the pre-ejection phase for two fundamentally different purposes. One is to first increase pressure in the chamber to a point where the outlet valve of the left ventricle will open. Essentially this is accomplished by contractile elements in the heart muscle which will exert an isometric pressure on blood in the chamber during the pre-ejection phase. The other is to eject the blood from the chamber, post pre-ejection phase, after the outlet valve of the chamber has been opened. This ejection of blood is accomplished by series-elastic elements of the heart muscle that shorten to effectively squeeze blood from the chamber through the open outlet valve.
From a mechanical perspective, because they must necessarily overlap somewhat during the pre-ejection phase, the combined action of the contractile and series-elastic elements of the heart muscle is two-fold. In tandem, the contractile elements initially exert an isometric pressure on the blood. This is preparatory to a subsequent, more efficient, ejection of blood from the chamber by the series-elastic elements. In this combination there is a balance between the two functions that will provide for a most efficient heart muscle contraction. Importantly, this balance needs to be established and maintained during the entire pre-ejection phase.
The beginning of the pre-ejection phase occurs when both the inlet and outlet valves of the chamber have been closed, and isometric pressure on blood in the chamber is initiated. It is an abrupt, sudden increase in isometric pressure that is characteristic of the beginning of the pre-ejection phase. From a metric standpoint, the abrupt, sudden increase in pressure at the beginning of the pre-ejection phase is detectable as a pressure discontinuity. Operationally, this pressure discontinuity is useable as a start point for employing mechanical techniques that will improve heart function during the pre-ejection phase.
With a weakened heart, which may result from any number of different reasons, the heart's ability to exert an isometric pressure during the pre-ejection phase is the first function to diminish its efficacy. The resultant imbalance in the application of forces on the heart's pumping chamber is detrimental to heart function. Consequently, the need to maintain an operational balance between the isometric pressure that is needed to open the chamber outlet valve, and providing the forces that are necessary for actually ejecting blood from the chamber, is essential for an efficiently operating heart.
In light of the above, it is an object of the present invention to provide a system and method for improving a heart muscle function that establishes and maintains a balance between isometric pressure on the pumping chamber of the heart during the pre-ejection phase, and the subsequent forces on the heart that eject blood from the pumping chamber. Another object of the present invention is to provide a system and method for improving heart muscle function by mechanically assisting in the preparation of a heart muscle contraction during the pre-ejection phase of a heart muscle pumping cycle. Still another object of the present invention is to provide a system for improving heart muscle function that is easy to manufacture, is simple to use and is comparatively cost effective.